In the field of telecommunications, systems for the detection of dial pulse signalling are well known. These systems commonly employ a method of detection based on the observance of rigid amplitude thresholds and signal timing constraints. Such systems have taken many forms, from electromechanical devices using relays to detect the presence of dial pulses, to solid state electronics and microprocessor controlled systems which perform the same function somewhat more economically.
However, a problem arises in that the dc component of dial pulse signalling, used for setting up switch paths in the exchange, is removed at the first transmission bridge encountered in the path. From there on, only the ac component, generated as a consequence of the pulse shape of the dc signalling, is available for detection at various distant points in the network. Moreover, in order to use these ac components to control distant apparatus, they must be detected reliably with adequate discrimination against similarly generated interfering signals (which arise due to cross-talk on telecommunications lines) as well as any other background noise normally present in all electrical circuits.
An added problem, as far as reliable detection of the ac component of the signalling pulses is concerned, is that of timing. In the UK the normal speed of a telephone dial is 10 impulses per second (ips) but because of manufacturing tolerances and wear, a range of 7-12 ips is specified. The variation in the speed of electronically produced dial pulses (such as from a push button telephone) will of course be much less. The effects of amplitude distortion must also be considered, where the amplitude of signalling pulses will vary according to the electrical characteristics of the transmission medium and the distance over which dial pulses are to be detected. The transmission medium will also affect the timing of the signalling pulses.
Prior art systems, therefore, which use as the basis of their detection method, fixed amplitude and timing thresholds, cannot provide a reliable solution to the above problems particularly when attempting to detect pulses at a considerable distance from the sending end.
The present invention provides a method and apparatus for detecting dial pulse signalling data which can be both flexible and reliable in use.
According to a first aspect of the present invention there is provided a method of detecting dial pulse signalling data in a received signal, comprising a training process and a recognition process, wherein the training process comprises processing of a portion of the received signal to extract characteristics of the received signal and said recognition process uses said characteristics to assist in detecting dial pulse signalling data in the received signal.
According to a second aspect of the present invention there is provided a detector for dial pulse signalling data comprising means for processing a portion of a received signal to extract characteristics of the received signal and operable using said characteristics to assist in detecting dial pulse signalling data in the received signal.
According to a a third aspect of the present invention there is provided interactive terminal equipment comprising a detector for detecting digits dialled, said equipment being adapted to transmit messages to the user inviting the user to dial digits according to the user's requirements and to provide a service to the user dependent on the digits dialled.